1. Field of the Invention
The present invention relates to method and apparatus for determining engine cycle timing using only a crankshaft angle (CA) sensor.
2. Related Art
A conventional four cycle engine is provided with a crankshaft angle sensor which generates a pulse signal every predetermined crank angle interval and a camshaft angle sensor which generates a pulse signal during each rotation of the camshaft (equivalent to two rotations of the crank shaft). A reference position of the camshaft is detected responsive to the output signal from the camshaft angle sensor. A crank angle is determined by counting the number of crank angle sensor pulse signals while a standard predetermined position of the camshaft is used as a reference. As a result, the state of all engine cylinders can be determined as a function of the crank angle.
In such conventional devices, however, since a camshaft angle sensor is needed in addition to the crankshaft angle sensor, there are disadvantages. For example, the structure of the device becomes complicated and manufacturing costs go up.
In an attempt to avoid these disadvantages, Japanese Patent Application Laid-Open No. Sho 60-240875 teaches that the stopped position of a crankshaft can be stored in a memory when the engine stops. After that, engine cycle timing is detected by using the stored stopped position when the engine is re-started. Ignition timing control and fuel injection timing control are performed based on the resultant engine cycle timing detection.
However, because a large compression force acts on an engine piston when it approaches top dead center (hereinafter, referred to as TDC), rotational torque after the engine is turned off may not be high enough to force the piston beyond TDC. As a result, the engine may actually reverse its direction slightly just before coming to a complete stop. Consequently, if the engine has so reversed, there is a difference between the actual stopped angle of the crankshaft and the stored stopped angle of the crankshaft. As a result, the determination of stopped engine state may be faulty due to the difference.
As another method to determine engine cycle timing without a signal from a camshaft angle sensor when an engine is re-startsd, Japanese Patent Application Laid-Open No. Hei 6-213052 discloses a device which cuts fuel injection to a specific cylinder and makes a determination depending on whether a misfire of that specific cylinder occurs or not. However, when causing the misfire intentionally by cutting fuel injection to a specific cylinder, engine torque fluctuation occurs and the device therefore has a disadvantage in that drivability of the engine deteriorates.